PolymerTEnTAFRågoR

Question 1

An extruded isotactic polypropylene homopolymer (Tg = -10 ºC; Tm = 165 ºC)
is completely transparent. What could be the cause? Could you recycle such a material?

Answer 1

Rapid cooling prevented crystallisation; yes, polypropylene is a thermoplastic polymer

Question 2

What is one similarity and one difference in structure between a thermoset and an
elastomer?

Answer 2

Similarity: they are both amorphous and crosslinked polymers; difference: crosslink density.

Question 3

State the accepted abbreviation and the minimum repetitive structural component of
polyvinyl chloride

Answer 3

Polyvinyl chloride - PVC. The repeating unit is C2H3CL

Question 4

Name the processing and, if is the case, the secondary shaping method for producing the plastic
parts in the figure below:
(1) Kevlar (Poly-paraphenylene terephthalamide) fibers for bullet-proof vests
(2) acrylonitrile butadiene styrene (ABS) shelf profiles
(3) ABS Lego sword
(4) ABS car rear spoilers

Answer 4

1) extrusion + fiber spinning; (2) extrusion; (3) injection molding; (4) injection molding.

Question 5

what is the role of the metering region of a single-screw extruder screw?

Answer 5

build up pressure.

Question 6

what are the main four units of an injection molding machine (

Answer 6

Injection unit, plasticating unit, mold and ejection unit.

Question 7

What does it mean that the viscosity function of a polymer melt is shear thinning?

Answer 7

Viscosity decreases with increasing shear rate

Question 8

Sketch the typical stress-strain diagram of an amorphous polymer at room temperature in a
short term tensile test. What causes the loss of linearity in the curve?

Answer 8

crazing (microcracks)

Question 9

Consider the structure of vinyl polymers: C2H3X

Give two examples of the side group X, specifying the chemical formula and the name of the polymer

How is the polydispersity index (dispersity) defined and explain its significance

Answer 9

E.g. X= H Polyethylene (PE), X = CH3 Polypropylene (PP), X = C6H5 Polystyrene (PS), X = Cl
Polyvinylchloride (PVC)

PDI (Ð) = Mw / Mn ,where Mw is the weight-averaged molecular weight and Mn is the number-
averaged molecular weight. (1p) PDI is a measure of how broad the molecular weight distribution
is.

Question 10

Sketch a typical viscosity function of a molten polymer. What molecular processes make the
viscosity function nonlinear?

Answer 10

The infinite-shear viscosity plateau can also be left out on grounds that it is difficult to reach in
polymer melts. Viscosity function (1p), correct labeling, incl. log-log (1p)

Question 11

Name the processing and secondary shaping method for producing a yarn of (continuous long)
carbon fibers.

Answer 11

extrusion (1p) with fiber spinning as secondary shaping (1p)

Question 12

Estimate the length of a fully extended polyethylene molecule knowing that:
Repeting Unit: C2H6

• the molecular weight of the entire molecule is M = 100000
• the molecular weight of the repeating unit is M = 28
• the distance between repeating units is 0.252 nm

Answer 12

n [number of repeating units] = 100000 / 28 = 3571; Estimated length = 3571 x 0.252 = 900 nm

Question 13

Name four types of polymer additives that are commonly mixed into polymers to improve their
properties (

Answer 13

Examples: fillers, flame retardants, stabilizers against thermal degradation, plasticizers,
antistatic agents, blowing agents, etc

Question 14

How can thin polymer fibers with highly oriented molecular structure be obtained?

Answer 14

Extrusion + fiber spinning as secondary shaping

Question 15

In what conditions could an amorphous polymer not exhibit crazing before fracture in a tensile
test?

Answer 15

At high loading rates and/or temperatures around and above Tg

Question 15

How does pressure affect the melting temperature of a semicrystalline polymer? Illustrate the
effect using a p-V-T diagram

Answer 15

The melting temperature increases with increasing pressure

Question 16

Define the average molecular weight of a polymeric material (1p). What does the molecular weight
quantify?

Answer 16

The molecular weight quantifies the length of polymer chains (1p). The average molecular weight
is defined as M = W / N

W = weight
N = number of atoms

Question 17

The strength of a material is determined by the forces holding it together. What are these forces
in polymer components and which one is considered to be dominant in determining their strength

Answer 17

There are two main forces that hold a polymeric material together: (i) covalent bonds that hold
together the C-C backbone (1p) and (ii) intermolecular Van-der-Waals forces (1p). The latter, (ii),
dominate the strength of plastics

Question 18

When a polymer is pumped through a die, the size of the polymer extrudate is greater than the
size of the die orifice, see Figure 1, phenomenon also known as ‘die swelling’. Briefly explain why
does ‘die swelling’ occur using a sketch or a short description.

Answer 18

After being stretched and oriented through the die, polymer molecules relax to a preferred state
when at atmospheric pressure, resulting in extrudate diameters greater than the die

Question 19

Name two secondary shaping operations for extrusion, and choose one secondary operation and briefly explain how the process works (sketch included)

Answer 19

Any two of: fiber spinning, film casting and film blowing (1p).

fiber spinning
A polymer melt is pumped through a circular die called a spinneret. Spinneret can
have up to 10 000 holes. The extrudates are drawn at a speed higher than the die
exit speed, resulting in thin filaments.

film casting
A polymer melt is extruded through a slit die unto a chill roll for
cooling wherefrom the film is being transported for storage.

Film blowing
A polymer met is extruded through an annular die and it is drawn and
inflated using an air supply blowing through the center of the annular
die.

Question 20

Name and write the chemical structure of a plastic material having at least 3 carbons and 5
hydrogen atoms in its repeating unit

Answer 20

polypropylene, polystyrene

Question 21

Is tacticity and long chain branching the same? Briefly explain

Answer 21

No. Tacticity refers to the positioning of side groups along the carbon backbone while long chain
branching refers to the presence of side chains

Question 22

What is the difference between a fossil-based polyethylene (PE) and a bio- PE manufactured
from sugar cane
- from chemical structure point of view (1p)
- from a sustainability point of view (advantage and disadvantage).

Answer 22

They are identical from chemical structure point of view. Bio-PE is manufactured from a
renewable resource but is not biodegradable

Question 23

En termoplast skall väljas till en produkt. Materialet behöver ha måttlig styvhet, god slagseghet i
temperaturområdet –20 till +40 C, god infärgbarhet, låg materialkostnad och vara välkänt vid
användning i rationella tillverkningsprocesser

Föreslå en lämplig typ av plast! Svara genom att ange fullständig benämning, vedertagen
förkortning och repeterande enhet

Vilken styvhet kan uppskattas för ditt föreslagna material enligt a), exempelvis vid korta
belastnings tider?

Answer 23

En lämplig typ av plast är polyeten, HDPE, CH2-CH2

tyvheten för HDPE är ca 1 GPa (0,7 – 1,5)

Question 24

Ange fullständig benämning och vedertagen förkortning för fyra härdplaster!

Answer 24

Fenolformaldehyd PF, Omättad polyester UP, Ureaformaldehyd UF och Melaminformaldehyd MF

Question 25

Beskriv fyra typer av ingenjörsmässiga termiska egenskaper, som kan användas om syftet är att
säkerställa funktionen hos en avsedd produkt vid en övre användningstemperatur! Svara med
benämning och en kortfattad beskrivning av hur egenskaperna mäts!

Answer 25

De ingenjörsmässiga termiska metoder som används är:
Formbeständighetstemperatur - Böjprov, avläser temperatur vid viss utböjning, 120 C/h
Formbeständighet enligt Martens – Böjprov, avläser temperatur vid viss utböjning, 50 C/h
Vicatpunkt – Avläser temperatur vid 1 mm intryckning av ett belastat cylindriskt stift, 50 C/h
UL-temperatur I (II-III) – Temperatur då alla (vissa) egenskaper förändras 50 % rel vid RT
Maximal användningstemperatur i luft resp. vatten – Industriella erfarenheter, för övrigt oklart

Question 26

Vad händer med materialet om användningstemperaturen överskrider de ovan nämnda
ingenjörsmässiga termiska egenskaperna?

Answer 26

Vid överskridande inträffar förändringar av egenskaper, främst av deformationsmotstånd och
termisk nedbrytning

Question 27

Beskriv huvudbeståndsdelarna i en formsprutningsmaskin! Beskriv också hur
formsprutningsprocessen går till genom att redogöra för vad som händer med råmaterialet
under hela tillverkningsförloppet.

Answer 27

Maskinen består huvudsakligen av sprutenhet, formlåsningsenhet och formverktyg. (0,5 p)
Förloppet är huvudsakligen smältning, transport (insprutning), trycksättning (formning i verktyg),
kylning i verktyg och utstötning.

Question 28

Redogör för de olika sekvenserna under en formsprutningscykel! Ange också vilka av
cykelsekvenser som ingår i total kyltid?

Answer 28

Insprutning, eftertryck, kylning och maskinrörelse (verktygsöppning, utstötning och
verktygsstängning). (1 p)
Total kyltid utgörs av eftertryckstid och maskininställd kyltid.

Question 29

Folieblåsning (eller filmblåsning) är en rationell metod för tillverkning av tunna plastfilmer.
Beskriv tillverkningsmetoden genom att redogöra för utrusningsdelar och det förlopp som
materialet utsätts för. Börja din redogörelse från utloppet av extrudern och avsluta med
upprullad film.

Answer 29

Utrustningsdelarna är blåshuvud, klämvalsar (med tillhörande ledplåtar) och
upprullningsanordning. (0,5 p)
Vid passagen genom blåshuvudet formas en slang av smältan som blåses upp med luft. Genom
uppblåsningen sträcks smältan ut och väggtjockleken reduceras kraftigt. Den utsträckta smältan
stelnar efter hand innan den når klämvalsarna. Klämvalsarna pressar dels samman filmen så att
ett inre övertryck kan hållas i blåsan och dels genererar en dragkraft i axiell led i blåsan.

Question 30

Write the chemical formula of polypropylene (PP). Note: pay attention to notation details

Answer 30

[CH2-CH4]n

Question 31

What general type of plastic are you dealing with that does not melt when heated and remains
relatively rigid

Answer 31

thermoset

Question 32

What does the degree of polymerization refer to?

Answer 32

How many repeating units there are

Question 33

What is the measurement unit for viscosity?

Answer 33

Pa⋅s

Question 34

Two polymer melts have had their melt flow index (MFI) determined in a lab: polymer A has
MFIA = 2 g/10 minutes and polymer B has MFIB = 13 g/10 minutes. Which polymer has higher
viscosity?

Answer 34

Polymer A

Question 35

What event marks the start of the injection molding cycle? And what dominates in terms of time
the injection molding cycle?

Answer 35

he mold closes. Solidification time

Question 36

What undesirable effect can be induced in an injection molded product if the injection
temperature is too high?

Answer 36

Thermal degradation

Question 37

name two types of polymers that exhibit brittle fracture and in what thermal conditions

Answer 37

ll polymers below Tg

Question 38

A polymer is labeled as biodegradable. What does that say about the possible raw materials they
could be made from?

Answer 38

It could either be made from fossil-based raw materials or renewable materials.
Polymera material